Int. Cl. A01n 17/00; A61k 9/04; 1301 13/02 US. Cl. 252-316 38 Claims ABSTRACT OF THE DISCLUSURE A process for encapsulating a hydrophilic liquid-in-oil emulsion with a wall-forming polymeric material comprising causing a coacervate solution of the wall-forming polymeric material to deposit about the hydrophilic liquidin-oil emulsion and hardening the capsule wall; also the capsular product produced from the aforedescribed process, which product is useful where ever there is need to maintain the hydrophilic liquid-in-oil emulsion in isolation from contiguous environment or there is need to control the release of the said emulsion through its capsular wall.

The subject matter of this applicataion is a continuation of Ser. No. 355,415, filed Mar. 27, 1964, now abandoned; said 355,415 being a continuation-in-part as to each of but claiming nothing more than is collectively disclosed in Ser. Nos. 781,919, 781,920, 781,921 and 781,922, all filed Dec. 22, 1958 and now abandoned.

This invention relates to a process of encapsulating minute particles en masse in a liquid manufacturing vehicle by forming liquid-liquid phases of wallforming polymer solution (e.g., coacervate) and equilibrium liquid (manufacturing vehicle), and to a capsule product having a core and a seamless protecting polymeric wall surrounding the core, said product resulting from the process. More particularly, the invention relates to a process for encapsulating hydrophilic liquid-in-lipophilic (oil) liquid emulsion particles including a step of forming a dispersed coacervate phase of the polymeric wall-forming solution in a continuous phase of equilibrium liquid as a vehicle.

The capsule-forming process of this invention involves the establishment of a system that is characterized as follows (these terms being defined below):

(1) It is in an agitated state.

(2) It comprises the following three phases, characterized by being mutually immiscible, but compatible, and further characterized, respectively, as being:

(b) a discontinuous phase of minute, mobile entities of emulsion particles (core material) comprising a hydrophilic liquid-in-oil emulsion dispersed in the vehicle, and having an anti-inversion agent in the oil, and

(c) a discontinuous polymeric-rich phase of minute, mobile entities of Wall-forming material dispersed in the vehicle.

This system results without more in a deposit of the wall-forming material around the entities of core material; the coacervate phase being capable of deposit around the dispersed entities of core material and also capable after deposit of maintaining itself as a wall against the shearing forces that exist as an incident of the required agitation of the system. The deposits quickly accumulate Patented Nov. 10, 1970 to a maximum thickness which may be varied by varying the amount of the wall material provided and the degree and type of agitation used, which may vary in accordance with the need for protection of the core material and the protective characteristics of the wall-forming material selected for use.

As employed herein, the term lipophilic is applied to those materials having relatively strong attractive forces for low dielectric constant and non-polar media. The term hydrophilic refers to those surfaces having relatively strong attractive forces for high dielectric constant and polar media.

In one form of the process of this invention, the capsules are prepared by first forming a primary hydrophilic liquidin-oil emulsion containing an anti-inversion agent in the oil to prevent inversion of said emulsion. The primary emulsion is then dispersed in a solution of the wall-forming polymeric material and a liquid-liquid phase separation (coacervation) caused to occur to thereby form three phases, the core material and two liquid phases comprising a coacervate of the wall-forming polymer and the equilibrium liquid thereof, whereupon the coacervate deposits about the dispersed primary emulsion particles.

Liquid-liquid phase separation refers, as used herein, to the separation of a solution (or a sol) of a wall-forming polymer or plurality of said polymers into two distinct liquid phases, one designated as the polymer-rich phase and the other the polymer-poor phase. For purposes of this application, the separated phase termed a solution of the wall-forming polymer includes a liquid phase wherein the Wall-forming polymer is present in the liquid in What is commonly referred to as the sol state. A coacervate is a polymer-rich solution which has separated from an original single-phase polymeric dispersion, leaving behind a polymer-poor solution or equilibrium liquid (vehicle). The coacervate appears initially as a fine dispersion of microscopic droplets of polymer in the equilibrium liquid (vehicle). When formed in a pure colloidal system, these droplets are essentially homogeneous. However, if minute foreign materials are dispersed in the system, the coacervate forms around these materials. Technically, the term coacervation therefore relates to the process by which the liquid colloidal concentrate or coacervate is formed as a phase entity of the initial sol or solution. In its practical aspect, and as employed herein, encapsulation by coacervation relates, in one aspect, to the process by which minute foreign materials present in the solution when the coacervate is formed are enveloped or encapsulated by the coacervate. Where the coacervate comprises a single wall-forming polymer, the process is termed simple coacervation; when more than one Wall-forming polymer is present in the coacervate and the different molecules are brought together by electric charges of opposite sign, the process is called complex coacervation. Complex coacervation, in one form of the invention, involves the separation of at least two wall-forming polymers of opposite electric charge to form the coacervate phase. Thus, after separation, one phase contains the said coacervating polymers in high concentration, and the other phase (equilibrium liquid) contains the polymers in relatively low concentration, these phases being known as the colloidrich phase and the colloid-poor phase, respectively.

It is essential that, if one or more of the Wall-forming polymers is temperature-gelable, the depositing or wrapping of the primary emulsion with the coacervate will be carried out at a temperature above the gel point of the gelable polymer. Moreover, in the case of complex coacervation, if one of the polymers be an isoelectric colloid, then the coacervation is carried out at a pH such that the polymer units of opposite electric charge are present.

While encapsulation of minute particles utilizing the phenomena of coacervation and the resultant coacervate phase has been described above in terms of effecting a phase separation from an initial wall-forming polymer solution and in the presence of the particles to be encapsulated, it is to be understood that the order of addition of the particles is not critical; i.e., the particles may be added to the system before or after the phase separation or coacervation has taken place. Moreover, once having established the relative amounts of the several components of the system that produce the coacervate state, appropriate amounts of the several materials comprising the coacervate-equilibrium liquid phases may be admixed and a coacervate state produced without need of forming an initial solution or sol of the wall-forming material.

The term hydrophilic liquid is intended to include water, aqueous solutions or suspensions, and non-aqueous solutions or suspensions immiscible in the oil phase of the primary emulsion.

Coacervation has long been known as a phenomenon primarily of academic interest, and only in recent years has it been developed for commercial utilization. U.S. Pat. Nos. 2,800,457 and 2,800,458 disclose methods for encapsulating oil droplets by coacervate coatings of the complex and simple types. This invention is an improvement over the aforementioned prior patents in that it provides a stable or intact hydrophilic liquid-in-lipophilic liquid emulsion entities for encapsulation by wall-forming polymers in coacervate form.

It has now unexpectedly been found that dispersed particle-entities consisting of a hydrophilic liquid-in-lipophilic (oil) emulsion may be encapsulated by a coacervate, if the oil phase contains a substance, herein designated an anti-inversion agent, capable of preventing the inversion of the hydrophilic liquid-in-oil emulsion to an oil-in-hydrophilic liquid emulsion in the course of the coacervate deposition and processing.

The present process and products resulting therefrom provide an improvement in the provision of impermeable coatings of high strength or coatings which permit a gradual release of contents for water-soluble materials broadly. For example, encapsulated emulsion particles can be prepared containing appropriate materials in the emulsion phases for use as sustained release fertilizers, plant growth hormones and pesticides such as fungicides, nematocides, bacteriocides, viricides and the like for agricultural use. In addition, ingredients can be incorporated in pre-mixed foods which could not normally be included because of loss in the drying process, the encapsulated ingredients being liberated by the shearing force exerted in a mixing step prior to actual use. Similarly, vitamins, notably combinations of water-soluble and oil-soluble vitamins, can be incorporated into dry cereal preparations for release in the body. Cosmetics can be prepared in which the topical agent is enclosed by impermeable but readily destructible coacervate shells. Pharmaceutical materials can be encapsulated for sustained release in the body upon contact with a predetermined pH environment or enzyme system, or where stability, odor, taste, or incompatibility problems are present. Such materials can be enclosed in coatings suitable for oral, topical, or injectable use by regulation of the particle size and coating thickness, permeability and hardness, or by selection of coating components. Insecticides with selective toxicity for insects but which are relatively non-toxic toward humans can be encapsulated, for example, with coacervate coatings which are highly impermeable except in the presence of enzymes of the insects. Rodenticides which are effective on ingestion by the animals but which have odors that forewarn or repel them can likewise be coated by the method of this invention with virtually complete impermeability with respect to the odor.

In addition to emulsions containing soluble or suspendable materials in the hydrophilic liquid phase, the coacervates herein, by practice of the present invention,

can be deposited about any emulsion particle-entity containing dissolved or suspended material in the oil phase. The ingredients to be dissolved or suspended in either the hydrophilic liquid or the oil phase of the primary emul sion are limited in selected only by the solubility, suspending characteristics, or compatibility of the ingredients. Moreover, the present process is applicable also to the encapsulation of particles already enclosed within a coacervate membrane-wall. Thus, in effect, a second coacervate wall can be prepared for the further protection of an already enclosed emulsion, a simple or complex coacervate being deposited over an existing simple or com plex coating.

As herein employed, the term primary emulsion refers to the hydrophilic liquid-in-oil'emulsion formed from the hydrophilic liquid, with or without dissolved or suspended ingredients, and the selected oil, with or without dissolved or suspended ingredients. The selection of said oil is not critical and is dependent on the function to be served by the oil; i.e., as a solvent or suspending medium in addition to its function as an external phase or merely as the external phase of the primary emulsion, provided, however, that said oil, with or without additives, should be substantially immiscible with the coacervate and equilibrium liquid. Thus, virtually any animal, vegetable, mineral, or synthetic oil having the desired physical characteristics can be employed for this purpose. Lanolin, corn oil, soy bean oil, castor oil, cod-liver oil, and mineral oil are examples of such oils. The conventional emulsifying agents, such as esters of polyhydric alcohols, sorbitan derivatives, and polyoxyethylene derivatives, are usually employed to facilitate the formation of the said primary emulsion. The HLB (hydrophile-lipophile balance) system, described in Remingtons Practice of Pharmacy, eleventh edition, Mack Publishing Company, 1956, p. 191, offers a convenient method for selection of the specific emulsifiers. Thus, by noting the HLB requirement for the particular emulsion system involved, an appropriate agent or combination of agents can be selected which will facilitate the formation and stabilization of the desired emulsion. As with all emulsion formation problems, selection of the most suitable agents must ultimately be based on trial. Accordingly, a sample of the emulsion should be checked, for example, by diluting and agitating with a relatively large volume of manufacturing vehicle to determine that a stable emulsion of the type desired has actually been obtained. Additionally, the selected emulsifying agents must be compatible with the formation of a co acervate.

The term anti-inversion agent includes any material capable of preventing the inversion of the primary hydro philic liquid-in-oil emulsion to an oil-in-hydrophilic liquid emulsion. Illustrative materials generally useful as antiinversion agents are (1) surface active agents, preferably those of the non-ionic type, and (2) oil-thickening agents such as the natural and synthetic waxes, solid fats, sterols, and other conventional oil-gelling or oil-thickening agents. Examples of the said surface active agents include the sorbitan fatty acid esters of the polyoxyethylene sorbitan fatty acid esters. The said oil-thickening agents include, for example, beeswax, carnauba wax, paraflin wax, saturated fatty acid esters, sistosterol, cholesterol, stigmasterol, and hydrogenated castor oil. In general, oil-thickening agents, including the oil-gelling agents suitable for use as anti-inversion agents are those which are retained in the oil, i.e., agents having a higher heat of immersion in the hydrophilic liquid than in the oil. Specifically to be mentioned is the use of ethyl cellulose as an anti-inversion agent in such hydrocarbon systems as water-in-xylene or water-in-benzene emulsions, as well as water-in-chlorinated hydrocarbon systems. Apparently, an ethyl cellulose film envelops both the hydrocarbon and water phases of such emulsions and affords a suitable surface on the external phase on which to deposit a coacervate of the type herein described. An exceedingly stable emulsion can be prepared in this manner. No generalization can be made regarding the amount of oil-thickening agent required as the anti-inversion agent in any given primary emulsion system, as the amount will vary with the specific oil included therein; routine testing of the stability of the desired emulsion on dilution with water will indicate the necessary concentration.

It has likewise been found that a further improvement in the efficiency of the encapsulating process as applied to hydrophilic liquid-in-oil emulsions and in the properties of the resulting encapsulated products can be realized by the addition of a hydrophilic thickening agent to the internal hydrophilic liquid to fix the dissolved or suspended material therein. Additionally, it has been found that the presence of such a thickening agent in the coacervating solution (hereafter defined) enhances the integrity of the several phases of the system, thereby minimizing further the loss of dissolved or suspended ingredients present in the primary emulsion.

The hydrophilic thickening agents used herein include materials which are substantially insoluble in the oil phase of the primary emulsion and are capable of increasing the viscosity of the internal hydrophilic liquid or of the coacervating solution. Suitable agents for this purpose embrace the known natural and synthetic thickening agents (including derivatives of both), specifically including those alluded to in Thickening Agents Used in Pharmacy, by Charles H. Becker, American Professional Pharmacist :939 (October) 1954, such as acacia, tragacanth, methyl cellulose, carboxymethylcellulose, magnesium aluminum siilcate, and the like, as well as other thickening agents such as the polyglycols, glycerin, syrups, and the like. The specific amounts of these materials may vary with the particular agent and system involved and can be readily determined by routine experimentation.

The primary emulsion is emulsified in the coacervating solution, which, preferably but not necessarily, contains a hydrophilic thickening agent of the type described above. Such thickening materials perform a role not fully understood, but their presence has been found to contribute substantially to the retention of dissolved or suspended ingredients in the respective phases of the primary emulsion during the process of coacervation.

The wall-forming material is a macromolecular polymer which has the property of being substantially immiscible with the external phase of the primary emulsion. Moreover, the wall-forming material should be capable of forming polymer-rich and polymer-poor liquid phases when in the environment of a solvent therefor and appropriate coacervating conditions.

Hereafter described, by way of illustrating the invention are coacervation techniques for forming capsular walls of polymeric material utilizing simple and complex coacervation system, each system in turn being illustrated by examples of natural synthetic polymers (colloids). While the invention is illustrated by describing coacervation procedures wherein the coacervation occurs in the presence of the primary emulsion, i.e., the primary emulsion is added to the system prior to coacervation, it is to be understood, as mentioned above, that the order of addition of the several components of the total system is not critical, nor is it critical to form an initial solution or sol of the wall-forming polymer and subsequently induce phase separation. It is within the scope of the invention to introduce the several materials at predetermined concentration under appropriate environmental conditions to establish coacervate-equilibrium liquid phases without resort to separation for an internal sol of the wall-forming polymer. Moreover, the systems described employ an aqueous vehicle phase, however, other equilibrium liquids may be employed, their solution being determined to meet the criteria of the system as broadly described above.

The term coacervating colloid refers to the wall-forming macromolecular polymer in an aqueous sol (including solution) which, on the occurrence of coacervation forms liquid colloid-rich and colloid-poor phases, the colloid-rich phase depositing about single or aggregated primary emulsion particleentities and the colloid-poor phase constituting the equilibrium liquid.

The term coacervating agent refers to materials or system environmental changes capable of initiating the separation of a colloid-rich phase and a colloid-poor phase from an original single phase colloidal sol (or solution) either alone or in combination. Examples of materials useful for initiating coacervation include (1) aqueous solutions of electrolytes, including organic and inorganic salts, e.g., salts having alkaline earth or alkalimetal cations, such as, sodium, ammonium magnesium, potassium, etc., and organic or inorganic anions such as sulfate, phosphate, acetate, formate, etc., and (2) liquids which are water-soluble and in which the coacervating colloid is less soluble than in water. A critical concentration exists for each coacervating agent below Which coacervation will not occur. This concentration may be determined for each combination of coacervating colloid and coacervating agent by routine testing.

The term coacervating solution applies to the sol (or solution) of the coacervating colloid, together with any coacervating agent, both as defined above, with or without a thickening agent, prior to the separation of the aforesaid colloid-rich phase (coacervate).

The term secondary emulsion refers to the emulsion formed when the primary emulsion is added to the coacervating solution before coacervation takes place. The said secondary emulsion is in effect an emulsion in an emulsion comprising the said primary emulsion dispersed in the coacervating solution and exists only until the coacervate deposits about the particles.

In the preparation of the primary emulsion, conventional emulsifying agents are normally employed, as previously indicated, to facilitate the establishment of and contribute to the stability of' the primary emulsion, as well as to assure that the correct type of emulsion, i.e., hydrophilic-liquid-in-oil, is obtained. Since the size of the ultimate capsules depends in part on the size of the droplets of the primary emulsion, the degree of dispersion of the hydrophilic liquid in the oil should be regulated in accordance with the desired particle size of the ultimate capsule.

The temperature at which the primary emulsion is prepared is of little consequence with respect to the functioning of the present process. However, in the case of a temperature gelable polymer it is necessary that the temperature at which wrapping of the primary emulsion is carried out be above the gel point of the wall-forming polymer. Where a thickening agent is added to thehydrophilic liquid of the primary emulsion, the temperature of the system should be within or closely approaching the gelling or thickening range of the thickening agent. For example where methyl cellulose is employed as the thickening agent, and a temperature gelable polymer is the wall-forming material, the temperature of the system should be about 50 C. After the coacervate has enveloped the emulsion entity particles, the temperature is lowered below the gel point of the coacervating polymer. Where gelatin is employed as the wall-forming polymer component, reduction in the temperature to 30 C. or lower, depending on the type of gelatin used, preferably to about 5 C., will produce the desired gelation.

As indicated previously, the secondary emulsion exists during the interval between the first contact of all ingredients of the coacervating solution and the actual formation of the coacervate. The secondary emulsion is a double emulsion consisting of discrete particles of the primary emulsion as the internal phase dispersed in the coacervating solution as the external phase. If the primary emulsion and the coacervating agent (in this instance, a substance that induces coacervation) are added to the aqueous solution of the coacervating colloid, the

double or secondary emulsion will persist until the concentration of the coacervating agent reaches the necessary level at which coacervation will occur. Where, for example, sodium sulfate solution is employed as the coacervating agent, the critical concentration with gelatin as the coacervating colloid has been found to be approximately 7%. However, where, as by the preferred sequence, the coacervating colloid and the primary emulsion are added to the coacervating agent, a sufficient concentration of the coacervating agent is present at all times during the said addition, and accordingly the secondary emulsion persists only for a short interval before coacervation takes place. Where the coacervating agent is a solvent in which the colloid is less soluble than it is in water, the solvent agent is added slowly to a mixture of the primary emulsion and the coacervating colloid with constant stirring to form the secondary emulsion. When the critical concentration range is reached for the particular colloid and solvent involved, coacervation will occur.

The ultimate size of the capsules produced is dependent in part, as heretofore indicated, on the degree of dispersion or size of the emulsion particles of the primary emulsion. In addition, the capsule size is of course a function of the thickness of the coacervate coating. Also of importance in this regard is the degree of dispersion of the primary emulsion and coacervating colloid in the coacervating agent. Where the primary emulsion is dispersed in a coacervating agent solution, the more complete and rapid the mixing, the smaller are the primary emulsion droplets that are presented as nuclei about which the coacervate wall will form, and hence the smaller will be the final capsule units.

The gelling or hardening step is significant with respect to the permeability of the coacervate membrane. In the case where the wall-forming polymer is a temperaturegelable polymer, the coacervate coating may be gelled by lowering the temperature below the gelation point. In the instance of non-temperature-gelable wall-forming polymers, the gelling of the coacervate walls may be induced, for example, by chemical additives which bring about further chemical reaction and consequent insolubilization of the wall-forming polymer. With many coacervate systems, instantaneous gelling of the warm coac ervate, as by adding the warm coacervate to ice water, produces a coacervate membrane having high permeability. A prolonged period of slow cooling also favors a membrane of high permeability. With many coacervate systems, the lowest permeability (or highest impermeability) is obtained with intermediate cooling rates. Thus, a highly impermeable coacervate coating is produced, in the case of a gelatin coacervate, on cooling the newlyformed coacervate to about degrees Centigrade over a period of approximately 30 minutes with continuous stirring. Optionally, the gelled coacervate walls may be further hardened, plasticized, or otherwise treated to adapt them to the intended use. Treating the gelled coacervate, gelatin, for example, with a 37% aqueous solution of formaldehyde under alkaline conditions for about one hour produces a coacervate wall which can then be dried.

Variations in the hardness of the coacervate wall can be obtained by varying the quantity of hardening agent and/or the period of contact therewith. Hardening likewise has considerable influence on the permeability of the coacervate, with respect both to the invasion of environmental fluids which would cause disintegration of the coating and to the containment of active ingredients which would otherwise impart undesirable odor or taste characteristics to the product.

The finally-treated coacervate can be separated by centrifuging, filtering, decanting, or the like. This can be followed by drying by known methods, as by spray drying, freeze drying, air drying, direct heating, and the like, optionally preceded by a Washing step, to obtain a prodnet essentially free of surface moisture. Such a product can then be formulated as a dry material.

A convenient and informative test for the integrity of a coacervate wall produced by the method of the present invention involves the incorporation of a soluble dye in the hydrophilic liquid phase of the primary emulsion. The coacervate is formed in the manner described, and the resulting material, after gelling and, optionally, after further hardening, is dispersed or immersed in the test liquid. The liquid is gently stirred to thoroughly expose all coacervate surfaces. Any dye escaping from the hydrophilic liquid phase through the coacervate shell is readily detectable in the test liquid.

Set forth hereafter are examples of several encapsulation systems broadly divided as to four categories according to the type of wall-forming polymer and type of coacervate, simple or complex.

EXAMPLE 1 A water-in-oil emulsion is prepared by emulsifying at 40 C. 10 ml. of water in which is dissolved 20 gm. of urea into 25 ml. of corn oil containing 0.25 gm. of hydrogenated castor oil. A sol of gelatin as the coacervating colloid is prepared by adding 10 gm. of gelatin to 100 ml. of water and heating to 40 C. Twenty grams of sodium sulfate is dissolved in ml. of water and this solution diluted to ml. with water. The emulsion and gelatin sol are heated to 40 C. and charged slowly in a confluent stream into the sodium sulfate solution, also heated to 40 C., the latter being agitated vigorously throughout the period of addition to disperse the incoming stream as soon as possible after its introduction, whereby to form a double emulsion of the oil particles (containing dispersed urea solution) in the coacervating solution. Coacervation occurs rapidly, and on completion of the phase separation the temperature of the equilibrium liquid containing the coacervate-coated emulsion is lowered to 5 degrees centigrade to gel the coacervate. Ten percent sodium hydroxide solution is added to raise the pH to 9.5. Ten milliliters of formaldehyde solution is added to the resulting product to harden the coacervate shell, and the mixture is allowed to stand for one hour at 5 degrees centigrade. The hardened coacervate is then separated from the mixture by centrifugation, washed, and spray-dried at 80 degrees centigrade (exhaust temperature).

The foregoing process is likewise operable with other anti-inversion agents substituted for the hydrogenated castor oil employed above; e.g., nonionic surface active agents and hydrophobic oil-thickening agents such as the natural and synthetic waxes, solid fats, sterols, and the like. Likewise, other oils can be selected as the external phase of the primary emulsion, and solutions of suspensions of other materials can be incorporated as the internal phase of the said emulsion. Instead of gelatin -as the coacervating colloid, other hydrophilic colloids, including agar-agar, albumen, alginates, casein, pectins, starch, fibrinogen, and the like, can be used. In addition to the sodium sulfate employed above, other solutions of electrolytes such as potassium chloride, sodium acetate, etc., or solvents such as alcohol, acetone, etc., are suitable as coacervating agents.

The products of this example find application as a source of nitrogen for agricultural use in which a prolonged release is desired.

EXAMPLE 2 Following the procedure of Example 1 but susbtituting the same quantities of cod-liver oil for the corn oil, lecithin for the hydrogenated castor oil, 3 gm. of ascorbic acid for the urea and potassium chloride for the sodium sulfate, there is produced a coacervate which can be incorporated in dry cereals.

EXAMPLE 3 A Water-in-oil emulsion is prepared by emulsifying at 50 C. 33 ml. of water containing 0.4 gm. of methyl cellulose into 33 ml. of mineral oil containing 0.33 gm. of sorbitan monooleate. A gelatin sol comprising 12.5 gm. of gelatin in 125 ml. of water is heated to 50 C., mixed with the emulsion, and added slowly to 125 ml. of a 20% ammonium phosphate solution, also heated to 50 C. The ammonium phosphate solution is vigorously stirred throughout the period of addition. The temperature of the mixture is lowered to 5 C. to gel the coacervate. Suificient sodium hydroxide solution is added to bring the pH to 9.5, followed by hardening of the coacervate with 12.5 ml. of 37% formaldehyde solution for 2 hours. The hardened coacervate is then filtered from the mixture, washed and dried.

Instead of inducing coacervation with ammonium phosphate solution, absolute ethyl alcohol, heated to 50 C., can be added slowly to the mixture of the emulsion and gelatin sol with constant and vigorous mixing. Coacervation occurs when the coacervating concentration range is reached, a total of approximately 150 ml. of ethyl alcohol being required.

The above-formed coacervates are highly impermeable to acid and alkaline solutions, as indicated by the small amount of dye lost to test liquids on prolonged exposure thereto.

EXAMPLE 4 A water-imoil emulsion is prepared by emulsifying at 40 G, into 37 gm. of lanolin containing 25 gm. of polyoxyethylene sorbitan monostearate, 30 ml. of water in which is dissolved 0.5 gm. of D. & C. Green No. 5. A gelatin sol comprising gm. of gelatin in 150 ml. of water is heated to 40 C. and thoroughly mixed with the emulsion and the resulting mixture introduced slowly into 150 ml. of a solution of sodium sulfate containing of acacia previously heated to 40 C. During the period of addition, the sodium sulfate solution is vigorously stirred. The temperature of the resulting equilibrium liquid containing the coacervate-coated emulsion is reduced to 5 C. and 15 ml. of 37% formaldehyde solution added to harden the coacervate shell. After two hours, the coacervate is separated from the equilibrium liquid, washed, and dried.

Substitution of 150 mg. of neomycin for the green dye above is productive of a coacervate which can be incorporated as dry, finely-divided granules in topical compositions of the ointment type by the usual methods.

EXAMPLE 5 An ethyl-alcohol-in-oil emulsion is prepared by emulsifying at 50 C., into 33 ml. of peanut oil containing 4 gm. of beeswax, 33 ml. of ethyl alcohol in which is dissolved 0.5 gm. of D. & C. Green No. 5 and 0.2 gm. of tragacanth. A fibrinogen sol is prepared at 50 C. from 12.5 gm. of fibrinogen and 125 ml. of water and is thoroughly mixed with the emulsion. The resulting mixture is added slowly to 125 ml. of a 20% barium chloride solution containing 37 gm. acacia, the barium chloride solution being vigorously agitated throughout the period of addition to facilitate coacervate formation. The temperature of the equilibrium liquid containing the coacervate-coated emulsion is lowered to 5 C. and 10% sodium hydroxide is added to give a pH of 9.5. Thereafter, 12.5 ml. of 37% formaldehyde is added to harden the coacervate shell. After standing for 5 hours, the resulting product is filtered from the mixture, washed and dried. Exposure of the above coacervate to acid and neutral test solutions indicates that a highly impermeable A glycerin-in-oil emulsion is prepared by emulsifying 75 ml. of glycerin at 50 C. into 75 ml. of peanut oil containing 0.75 gm. of hydrogenated castor oil. A gelatin sol is prepared from 50 gm. of gelatin in 500 ml. of Water heated to 50 C. The sol is mixed with the said emulsion and the resulting mixture added slowly to 500 ml. of a 20% sodium sulfate solution, also heated to 50 C. The sodium sulfate solution is vigorously stirred throughout the period of addition. The temperature of the mixture is then lowered to 5 C. to gel the coacervate. Suflicient 10% sodium hydroxide solution is then added to bring the pH to 9, and 50 ml. of 37% formaldehyde is introduced to harden the coacervate shell. After 4 hours, the hardened coacervate is then filtered from the mixture, washed and air dried at C.

In addition to glycerin as the dispersed phase of the primary emulsion, as illustrated above, other nonaqueous solutions or suspensions immiscible in the oil phase can be used. Similarly, with such other emulsion systems other anti-inversion agents such as nonionic surface active agents and oil-thickening agents, e.g., natural and synthetic waxes, solid fats, sterols and the like, can be substituted for hydrogenated castor oil employed above.

EXAMPLE 7 A water-in-oil emulsion is prepared by emulsifying at 40 C. 2 ml. of water into 20 ml. of soybean oil containing 0.2 gm. of magnesium aluminum silicate. A gelatin sol containing 10 gm. of gelatin in ml. of water is thoroughly mixed with the said emulsion, heated to 40 C., and the resulting mixture added slowly, with continuous agitation, to ml. of 98% methanol of 40 C. The temperature of the resulting equilibrium liquid containing the coacervate-coated emulsion is then reduced to 5 C. and 12 ml. of 37% formaldehyde solution added to harden the coacervate shell. Aft-er standing for 5 hours, the coacervate is separated from the equilibrium liquid, washed and dried.

Other anti-inversion agents can be substituted for the agent employed above, e.g., nonionic surface active agents and oil-thickening agents such as natural and synthetic waxes solid fats, sterols and the like. Also other oils can be selected as the external phase of the primary emulsion, and nonaqueous coacervating agents other than methanol can be employed, the latter being those solvents in which the coacervating colloid (e.g., gelatin, as above, or other gelable hydrophilic colloids) is less soluble than it is in water.

Complex coacervation employing at least one natural polymer and at least one temperature gelable polymer The following examples show suitable polymer combinations for complex coacervation.

EXAMPLE 1 A water-in-oil emulsion is prepared by emulsifying at 40 C. a solution of 25 gm. of urea in 25 ml. of water into 40 ml. of peanut oil containing 5 gm. of beeswax. A sol is prepared by dissolving at 40 C. 27 gm. of gum acacia and 20 gm. of gelatin in 350 ml of water. With continuous stirring, the emulsion is added to the sol to form a double emulsion of the oil droplets containing dispersed urea solution in the sol. To the emulsion-sol mixture is added, dropwise and with containous stirring, 600 ml. of water previously heated to 40 0, thereby causing the coacervate to form. The temperature of the coacervating medium is lowered to 5 C. to gel the coacervate. Sufiicient 10 percent sodium hydroxide solution is added to raise the pH to about 10, and 20 ml.

1 1 of 37 percent formaldehyde solution is added to the resulting product to harden the coacervate shell. The mixture is allowed to stand for 4 hours at C. The hardened coacervate is then separated from the mixture by centrifugation, washed and dried.

The above composition can be employed as a fertilizer in which the nitrogen is made available over a prolonged period through slow release of the urea.

Other aqueous solutions and aqueous suspensions or water and oil-insoluble ingredients can likewise be employed as the hydrophilic liquid of the primary emulsion above.

Instead of diluting the emulsion-sol mixture to cause formation of the coacervate, coacervation can be induced by adjusting the pH to th coacervating range.

The foregoing process is likewise operable with other anti-inversion agents substituted for the beeswax employed above, e.g., nonionic surface active agents and hydrophobic oil-gelling or oil-thickening agents such as natural and synthetic Waxes, hydrogenated castor oil, solid fats, sterols, and the like. Likewise, other oils can be selected as the external phase of the primary emulsion. Instead of gelatin and gum acacia as the coacervating colloids, other combinations of hydrophilic colloids can be used, such combinations being selected from among such colloids, as agar-agar, albumen, alginates, casein, pectins, starch, fibrinogen, and the like. In selecting the colloid combination, it should be remembered that one colloid must be gelable and one must be an isoelectric colloid.

EXAMPLE 2 A suspension of 100 gm. of micronized caffeine in 100 ml. of water is prepared at 50 C. A mixture of 50 gm. of sitosterol and 150 ml. of corn oil is likewise prepared at 50 C. The caffeine suspension is emulsified into the oil mixture by passing the materials together through a colloid mill. Two hundred grams of collagen and 200 gms. of sodium alginate are dispersed in 8 liters of water and heated to 50 C. The resulting dispersion is raised to pH 7 with sodium hydroxide solution. With continuous stirring of the collagen-alginate sol, the caffeinecorn oil emulsion is dispersed therein. Stirring is continued for 10 minutes with the temperature maintained 50 C. Dilute acetic acid is then added dropwise with continuous stirring to lower the pH to 3.2. Stirring is continued for an additional minutes and the resulting coacervative is cooled to 5 C. over a period of 30 minutes, separated by centrifuging and freeze dried at 40 C.

EXAMPLE 3 A suspension of 0.5 gm. of methyl cellulose is prepared in 50 ml. of water containing 0.5 gm. of D. & C. green dye No. 5. The suspension is then heated to 60 C. To 25 ml. of white mineral oil is added 0.25 gm. of sorbitan monooleate and the resulting oil solution heated to 60 C. The aqueous liquid is emulsified into the oil by homogenization. Forty grams of cationic starch and gm. of carboxymethylcellulose are dispersed in 1500 ml. of water and the resulting sol heated to 60 C. Sufficient 10% sodium hydroxide is then added to raise the pH to 6.5. The emulsion is then dispersed in the starchcarboxymethylcellulose solution with continuous stirring at 60 C. for 30 minutes. The pH of the resulting secondary emulsion is lowered to 3.8 with 10% hydrochloric acid, stirring being continued at 60 C. for an additional 30 minutes. The resulting coacervate is cooled to 10 C. over a period of 30 minutes, filtered, washed and air dried at 90 C.

EXAMPLE 4 A water-in-oil emulsion is prepared by emulsifying at 50 C. 50 ml. of water in which is dissolved 0.5 gm. of D. & C. green dye No. 5 and 0.5 gm. of methyl cellulose into 50 ml. of mineral oil containing 0.5 gm. of sorbitan monooleate. A sol comprising 25 gm. of gum acacia and 25 gm. of gelatin in 300 ml. of water is heated to 50 C. The emulsion is added to the sol with continuous stirring. Seven hundred milliliters of water, previously heated to 50 C. is added dropwise with continuous stirring to the emulsion-sol mixture. The temperature of the mixture is lowered to 5 C. to gel the coacervate. Sufficient 10% sodium hydroxide solution is added to bring the pH up to 9.5, followed by the addition of 25 ml. of 37% formaldehyde solution. The hardened coacervate is then filtered from the mixture, washed and dried.

EXAMPLE 5 A water-in-oil emulsion is prepared by emulsifying at 50 C. ml. of water in which is dissolved 0.75 gm. of D. & C. green dye No. 5 and 0.75 gm. of tragacanth into 75 ml. of mineral oil containing 1.0 gm. of hydrogenated castor oil. A sol is prepared at 50 C. from 50 gm. of gelatin, 30 gm. of gum acacia, 20 gm. of carboxymethylcelluolse, and 600 ml. of Water. The emulsion is added slowly to the sol with continuous stirring. To the emulsion-sol mixture is added dropwise 1500 ml. of water, previously heated to 50 C., to gel the coacervate. Sufficient 10% sodium hydroxide solution is added to bring the pH to about 9.5, and 50 ml. of formaldehyde solution is introduced to harden the coacervate shell. The hardened coacervate is then separated from the coacervating medium by centrifugation, washed, and dried.

EXAMPLE 6 A glycerin-in-oil emulsion is prepared by emulsifying at 50 C. 50 ml. of glycerin into 50 ml. of peanut oil containing 0.5 gm. of hydrogenated castor oil. A sol is prepared from 27 gm. of gum acacia and 20 gm. of gelatin in 350 ml. of water heated to 50 C. The emulsion is added slowly to the sol with continuous stirring. To the emulsion-sol mixture is added dropwise 650 ml. of water previously heated to 50 C. The temperature of the mixture is lowered to 5 C. to gel the coacervate. Sufficient 10% sodium carbonate solution is introduced to raise the pH of the mixture to about 9.5, and 20 ml. of 37% formaldehyde solution is added to harden the coacervate shell. The then hardened coacervate is separated from the mixture by centrifugation, washed, and dried.

EXAMPLE 7 Two grams of tragacanth and 0.6 gm. of D. & C. green dye No. 5 are dispersed in 60 ml. of glycerin, and the dispersion is heated to 40 C. Twenty grams of paraffin wax are added to 40 gm. of petrolatum and the resulting mixture heated to 40 C. The glycerin solution is emulsified into the paraffin-petrolatum mixture. A dispersion of 50 gm. of serum albumin is prepared in 250 ml. of water and heated to 40 C. Sufificient 20% acetic acid is added to bring the pH to 3.0. The emulsion is then dispersed into the albumin sol with continuous stirring. Thereafter, 50 gm. of acacia is dispersed in 250 ml. of water and heated to 40 C. The pH of the resulting dispersion is adjusted to 3.0 with 20% acetic acid. The acacia sol is added dropwise to the emulsion mixture with continuous stirring. Immeriately thereafter, 700 ml. of water previously heated to 40 C. is added dropwise, the temperature being maintained at 40 C. and stirring continued for 30 minutes. The resulting coacervate is cooled to 4 C., filtered, washed and dried.

Simple coacervation employing a synthetic polymer The synthetic polymers employed are those in which the polymer units comprise both lipophilic and hydrophilic units, i.e., one class of recurring polymer unit is essentially lipophilic in character, e.g., one derived from styrene, an alkyl ring-substituted styrene, an ether, ester or a halogen ring-substituted styrene, an ether or estersubstituted ethylene, and the other major recurring unit is essentially hydrophilic in character, e.g., derived from maleic acid, maleic acid amide, acrylic acid, crotonic acid, or acrylic acid amide. In combination, these lipophilic and hydrophilic units preferably comprise a majority of the polymeric units present in the polymer. Other polymer units may also be present in the copolymer, so long as they are present in minor amounts, i.e., less than either the hydrophilic or lipophilic copolymer units. Included among these copolymers are the hydrolyzed styrene-maleic anhydride copolymers, styrene-maleic acid amide copolymers, the sulfonated polystyrenes, the carbohydrate acetate phthalates, e.g., starch acetate phthalate, cellulose acetate phthalate and amylose acetate phthalate, polymethacrylic acid, methylvinyl ethermaleic acid copolymer.

Preferred among the polymers employed in this invention are the hydrolyzed styrene-maleic anhydride copolymers, the anhydride groups of which are preferably at least 50% hydrolyzed. The copolymer can also contain other polymer units in minor amounts, e.g., those derived from acrylonitrile, acrylic acid, methacrylic acid, itaconic acid, ethyl vinyl ether, methyl vinyl ether, vinyl chloride, vinylidene chloride, etc., and the like. As used in the present specification, the term hydrolyzed styrene-maleic anhydride copolymer is meant to include these modifications as Well as other modifications in the structure and method of preparation which do not alter the essential lipophilic and hydrophilic properties of the copolymer.

The preferred copolymers of the present invention can be represented by the following formula:

wherein R represents lipophilic polymer units of which more than 70% are styrene residues, the other remaining residues, when present, being those of acrylonitrile, acrylic acid, methacrylic acid, itaconic acid, vinyl chloride, vinylidene chloride, and the like, and R represents hydrophilic polymer units of which more than 50% are maleic acid units, preferably more than 70% with the ratio of R to R being from 1:1 to about 4: 1, preferably from 1:1 to about 1.2: 1, and n is an integer from about 90 to about 1000. The average molecular weight of the copolymer ranges preferably from about 20,000 to about 200,000.

Copolymers employed in this invention are well known in the art. For example, styrene-maleic anhydride copolymer and Resin SC2 (the latter being a modified styrenemaleic anhydride copolymer available from Monsanto Chemical Company) can be hydrolyzed to obtain a styrene-maleic acid copolymer. The hydrolysis of the acid anhydride linkages to a-dicarboxylic acid units. It is preferred that the hydrolysis be substantially complete, i.e., more than about 50% complete.

The solubility of the polymers employed in this inven tion varies considerably in selected hydrophilic liquids. For example, completely hydrolyzed styrene-maleic anhydride copolymer is about 2% soluble in water but at least 20% soluble in a 50:50 mixture of methanol and water. Thus, the desired amount of copolymer can be contacted with the lipophilic material by high dilutions in water or, preferably, by the addition of a solubilizing agent, e.g., another hydrophilic liquid. A type of solubilizing agent useful when carboxylic acid polymers are employed are the polysaccharides, e.g., alginates, pectins, methyl cellulose, carboxymethylcellulose, etc. Of particular usefulness are the galactose polysaccharides, e.g., those derived from Irish moss (carrageen), available as Sea- Kem Type No. 1 from Seaplant Chemical Corporation, New Bedford, Mass. For example, the solubility of completely hydrolyzed styrene-maleic anhydride copolymer in water can be raised from about 2% to about 7 to 10% in the presence of relatively small amounts of this polysaccharide, e.g., one part to four parts of the copolymer.

Between pH 1 and 2.5 (the pH of the normal stomach) a styrene-maleic acid copolymer as defined herein is only to 1% ionized and thus is insoluble over this pH range, making the said polymer useful as an enteric coating.

14 EXAMPLE 1 A water-in-oil emulsion is prepared by emulsifying at C. in 10 ml. of water in which is dissolved 20 gm. of urea into 25 ml. of corn oil containing 0.25 gm. of hydrogenated castor oil. A $01 of styrene-maleic acid copolymer is prepared by adding 10.0 gm. of the said copolymer to 500 ml. of water. Twenty grams of sodium sulfate is dissolved in 80 ml. of water and this solution diluted to ml. with water. The emulsion and polymer sol are heated to 80 C., and charged slowly in a confluent stream into the sodium sulfate solution, also heated to 80 C., the latter being agitated vigorously throughout the period of addition to disperse the incoming stream as soon as possible after its introduction, whereby to form a double emulsion of the oil particles containing dispersed urea solution in the coacervating solution. Coacervation occurs rapidly, and on completion of the phase separation the temperature of the equilibrium liquid containing the coacervate-coated emulsion is lowered to 5 C. to gel the coacervate. Five milliliters of glacial acetic acid is added to the resulting product to harden the coacervate shell, and the mixture is allowed to stand for 4 hours at 5 C(The hardened coacervate is then separated from the mixture by centrifugation, washed and spray-dried at 80 C. (exhaust temperature).

Aqueous suspensions of waterand oil-insoluble ingredients can also be employed as. the water phase of the primary emulsion above.

Dilution of a mixture of the emulsion and the polymer sol, with vigorous agitation, with dioxane as the coacervating agent instead of sodium sulfate gives an equally satisfactory product.

The foregoing process is likewise operable with other anti-inversion agents substituted for the hydroxylated castor oil employed above, e.g., nonionic surface active agents and oil-gelling or oil-thickening agents such as natural and synthetic waxes, solid fats, sterols and the like. Likewise, other oils can be selected as the external phase of the primary emulsion, and solutions or suspensions of other materials can be incorporated as the internal phase of the said emulsion. Instead of styrenemaleic acid copolymer as the coacervating polymer, other linear macromolecular synthetic polymers such as those previously described can be used. In addition to the sodium sulfate employed above, other solutions of electrolytes such as potassium chloride, sodium acetate, etc., or solvents such as alcohol, acetone, etc. are suitable as coacervating agents.

The products of this example find application as a source of nitrogen for agricultural use in which a prolonged release over a long period of time is desired.

EXAMPLE 2 Following the procedure of Example 1 but substituting the same quantities of soybean oil for the corn oil, lecithin for the hydrogenated castor oil, a green dye solution (D. & C. Green No. 5) comprising 0.5 gm. of dye dissolved in the water for the urea, cellulose acetate phthalate for the styrene-maleic acid, and potassium chloride for the sodium sulfate, there is produced a coacervate in which only a small amount of green dye is observable in the equilibrium liquid, the major portion being encapsulated by the coacervate.

EXAMPLE 3 A water-in-oil emulsion is prepared by emulsifying at 80 C. 33 ml. of water containing 0.5 gm. of D. & C. Green No. 5 and 0.2 gm. of magnesium aluminum silicate into 33 ml. of mineral oil containing 0.33 gm. of corbitan monooleate. A sol comprising 8.0 gm. of styrenemaleic acid amide copolymer in 400 ml. of water is heated to 80 C., mixed with the emulsion and added slowly to ml. of a 20% sodium phosphate solution, also heated to 80 C. The sodium phosphate solution is vigor- 15 ously stirred throughout the period of addition. Fifteen milliliters of 10% hydrochloric acid solution is added to harden the coacervate. The hardened coacervate is then filtered from the mixture, Washed and dried.

The above-formed coacervate is highly impermeable to acid and neutral solutions, as indicated by the small amount of dye lost to test liquids on prolonged exposure thereto.

Other thickening agents for the internal phase, such as acacia, tragacanth, etc., can be substituted for the magnesium aluminum silicate above.

EXAMPLE 4 A glycerin-in-oil emulsion is prepared by emulsifying at 80 C. 100 ml. of glycerin into 100 ml. of peanut oil containing 1 gm. of hydrogenated castor oil. A styrenemaleic acid copolymer sol is prepared from 100 gm. of polymer in 5000 ml. of water heated to 80 C. The sol is mixed with the said emulsion and the resulting mixture added slowly to 1200 ml. of a 20% sodium sulfate solution, also heated to 80 C. The sodium sulfate solution is vigorously stirred throughout the period of addition. To the resulting coacervate is added 200 m1. of 38% acetic acid to harden the coacervate shell. The hardened coacervate is then filtered from the mixture, and dried.

In addition to glycerin as the dispersed phase of the primary emulsion, as illustrated above, other non-aqueous solutions or suspensions immiscible in the oil phase can be used. Similarly, with such other emulsion systems other anti-inversion agents such as nonionic surface active agents and hydrophobic oil-gelling or oil-thickening agents, e.g., natural and synthetic Waxes, solid fats, sterols and the like, can be substituted for the hydrogenated castor oil employed above.

Dissolve 100 gm. of chloral hydrate in 50 ml. of water and heat to 70 C. Dissolve 25 gm. of beeswax in 125 ml. of mineral oil at 70 C. Emulsify the aqueous solution into the oil solution by passing the combined mixture through a hand homogenizer 4 times. Disperse 75 gm. of styrene-maleic acid copolymer in 1500 ml. of water, heat to 70 C. and add sufiicint sodium hydroxide to dissolve the copolymer. (At this point the copolymer solution has a pH between 7 and 8). With continuous agitation, disperse the emulsion in the copolymer sol. Dissolve 75 gm. of gelatin in 500 ml. of water at 70 C. and add 10% sodium hydroxide to raise the pH of the sol to 7. Add the gelatin sol dropwise to the copolymer-emulsion mixture with continuous stirring. Immediately thereafter, with the temperature at 70 C. and with continuous stirring, add dropwise 20% acetic acid solution to bring the pH of the mixture down to 4.5. Maintain the mixture at 70 C. with stirring for 30 minutes, and then cool to 6 C. over a period of 30 minutes. Maintain the material below 10 C. for 1 hour. Add 75 ml. of 37% formaldehyde solution followed in 1 hour by a sufiicient amount of 10% sodium hydroxide to bring the pH up to 8. The coacervate is then filtered, washed with water, and freeze-dried at 40 C.

The foregoing process is likewise operable with other anti-inversion agents substituted for the beeswax employed above, e.g., nonionic surface active agents and oilgelling or oil-thickening agents such as natural and synthetic waxes, hydrogenated castor oil, solid fats, sterols, and the like. Likewise, other oils can be selected as the external phase of the primary emulsion. Instead of gelatin and styrene-maleic acid copolymer as the coacervating 16 polymers, other combinations can be used, such combinations being selected from among such colloids as agaragar, albumen, alginates, casein, pectins, starch, fibrinogen and such synthetic polymers as starch acetate phthalate, cellulose acetate phthalate and deacetylated chitin.

Dissolve 1.5 gm. of D. & C. Green No. 5 in 150 ml. of water at 50 C. Dissolve 1 gm. of hydrogenated castor oil in 100 ml. of corn oil at 50 C. Emulsify the aqueous solution into the oil by passing the combined liquids through a hand homogenizer four times. Disperse 50 gm. of cellulose acetate phthalate in 700* gm. of Water at 50 C., and add a sufficient amount of 10% sodium hydroxide to raise the pH of the solution to between 7 and 8. Disperse 50 gm. of bovine fibrinogen in 700 ml. of cold water and heat to 50 C. Add a sufficient amount of 10% sodium hydroxide to bring the pH of the fibrinogen dispersion up to between 7 and 8. Combine the cellulose acetate phthalate solution and the fibrinogen solution and disperse the emulsion in these combined solutions with continuous agitation. Immediately after the addition of the emulsion, add dropwise a sufficient amount of 10% hydrochloric acid to bring the pH of the mixture down to 3.0. At this point, leave the mixture stirring at 50 C. for 30 minutes. Then cool to 5 C. over a period of 30 minutes. Add 50 ml. of 37% formaldehyde solution followed in 2 hours by sufficient 10% sodium hydroxide to bring the pH to 8.5. The coacervate is then centrifuged, washed and dried in air at C.

Suspend 25 gm. of rotenone in 50 ml. of glycerin at 60 C. Emulsify the glycerin suspension into the oil by passing the combined mixture through a homogenizer. Dissolve 50 gm. of styrene-maleic acid amide copolymer in 400 ml. of water at 60 C. Add 20% acetic acid to adjust the pH to 3.0. Disperse 50 gm. of serum albumin in 300 ml. of cold water and heat to 60 C. Add 20% acetic acid to adjust the pH to 3.0. Combine the copolymer solution with the albumin sol and disperse the emulsion therein with continuous agitation. Add dropwise 400 ml. of water, previously heated to 60 C., to complete the phase separation. Then cool the mixture to 4 C. over a period of 30 minutes and leave at this temperature for one hour. Harden with 50 ml. of 37% formaldehyde solution for 1 /2 hours. Filter, wash and dry the hardened coacervate in air at 80 C.

EXAMPLE 4 A water-in-oil emulsion is prepared by emulsifying at 70 C. a solution of 25 gm. of urea in 25 ml. of water containing 0.2 gm. of methyl cellulose into 40 ml. of peanut oil containing 5 gm. of beeswax. Twenty grams of styrene-maleic acid copolymer is dispersed in 800 ml. of water at 70 C., and 10% sodium hydroxide solution is added to raise the pH of the copolymer dispersion to 7. The emulsion and copolymer solution are thoroughly mixed, and to this mixture is added, slowly and with stirring, at sol of 20 gm. of gelatin dispersed in ml. of water at 70 C., the temperature throughout the addition at 70 C. Approximately 50 ml. of 1.0 N hydrochloric acid is added dropwise and with stirring to the foregoing emulsion to bring the pH to 4.9. On formation of the coacervate, 25 ml. of pyruvic aldehyde is added 1 7 to harden the coacervate shell, and the thus hardened coacervate is then centrifuged and spray dried at 80 C. (exhaust temperature).

The coacervate above can be used as a source of nitrogen for soil, the encapsulated urea being slowly released over a prolonged period.

water at 55 C. and add sufiicient acetic acid to adjust the pH to 3.0. Disperse 75 gm. of serum albumin in 450 ml. of cold Water, heat to 55 C. and add a sufiicient amount of 20% acetic acid to adjust the pH to 3.0. Combine the copolymer solution with the albumin sol and disperse the emulsion therein with continuous agitation. Add dropwise 600 ml. of water, previously heated to 55 C. Leave stirring for 30 minutes at 55 C., then cool to 4 C. over a period of 30 minutes and leave at this temperature for one hour. Harden with 75 ml. of 37% formaldehyde for 2 hours. Filter, wash and dry the harden coacervate.

Mix 1 gm. of D. & C. Green No. 5 and 3 gm. of tragacanth and disperse the mixture in 100 ml. of propylene glycol at 80 C. Dissolve 25 gm. of beeswax in 50 ml. of peanut oil at 80 C. Emulsify the glycol into the oil uti lizing a homogenizer. Mix 25 gm. of SeaKem Type No. 1 (a galactose polysaccharide) with 100 gm. of styrenemaleic acid copolymer and disperse the mixture in 1800 ml. of water at 80 C. With continuous stirring, disperse the emulsion in the copolymer dispersion. Dissolve 100 gm. of gelatin in 2000 ml. of water at 80 C. with continuous stirring, add the gelatin sol dropwise to the copolymer-emulsion mixture. Continue stirring at 80 C. for minutes, then cool to below 10 C. over a period of 30 minutes. Leave stirring at this temperature for one hour. Harden with 37% formaldehyde for 2 hours, wash and dry.

What is claimed is:

1. A process for coating particles of a hydrophilicliquid-in-oil emulsion by coacervation, comprising:

(a) establishing an agitated system comprising a liquid vehicle forming a continuous first phase, a second phase dispersed therein consisting of minute, mobile entities of a hydrophilic-liquid-in-oil emulsion having an anti-inversion agent in the oil phase, and a third phase dispersed in said first phase and comprising a coacervate solution of a wall-forming polymeric material, the said three phases being mutually immiscible but compatible and said first and third phases being maintained in a coacervate-equilibrium liquid relationship by the presence of a coacervating agent whereby the coacervate deposits about the emulsion particles; and

(b) harden the coacervate deposit so formed.

2. A process for coating particles of a hydrophilicliquid-in-oil emulsion by coacervation, comprising:

(a forming a primary hydrophilic-liquid-in-oil emulsion having an anti-inversion agent in the oil phase;

(b) admixing said emulsion and an aqueous solution of a hydrophilic wall-forming polymer to form a secondary emulsion wherein. the solution is the continuous phase;

(c) causing a coacervate of the wall-forming polymer to separate from the solution and to deposit about the hydrophilic liquid-in-oil emulsion particles; and

(d) hardening the coacervate deposit so formed.

3. A process in accordance with claim 2 wherein the coacervate is formed by introducing the primary emulsion and the aqueous sol of the hydrophilic polymer into an aqueous solution of a coacervating agent.

4. A process for coating particles of hydrophilic liquidinoil emulsion by coacervation which comprises:

(a) forming a primary hydrophilic liquid-in-oil emulsion having an anti-inversion agent in the oil phase,

(b) admixing the said primary emulsion and an aqueous sol of a temperature-gelable hydrophilic wallforming polymer to form a secondary emulsion wherein the sol is the continuous phase;

(c) causing a coacervate of the hydrophilic polymer to separate from the sol and to deposit around the particles of the emulsion at a temperature above the gel point of said polymer; and

(d) hardening the coacervate deposit so formed by lowering the temperature below the gel point of the gelable wall-forming polymer.

5. The process of claim 4 wherein the coacervate is formed by introducing the primary emulsion and the aqueous sol of the hydrophilic polymer into an aqueous solution of a coacervating agent.

6. The process for coating particles of a hydrophilic liquid-inoil emulsion by coacervation which comprises:

(a) forming a primary hydrophilic liquid-in-oil emulsion having an anti-inversion agent in the oil phase;

(b) admixing the said emulsion and an aqueous sol of at least two hydrophilic wall-forming polymers to produce a secondary emulsion wherein the sol is the continuous phase;

(c) causing a complex coacervate to separate from the sol and to deposit about the particles of the primary emulsion; and

(d) hardening the coacervate deposit so formed.

7. The process of claim 6 wherein the coacervate is formed by introducing the primary emulsion and the aqueous sol of the hydrophilic polymer into an aqueous solution of a coacervating agent.

8. A process for coating particles of a hydrophilic liquid-in-oil emulsion by coacervation which comprises:

(a) forming a primary hydrophilic liquid-in-oil emulsion having an anti-inversion agent in the oil phase;

(b) admixing the said primary emulsion and an aqueous sol of at least two hydrophilic wall-forming polymers, at least one of which is temperature gelable and at least one of which is isoelectric, to produce a secondary emulsion wherein the sol is the continuous phase;

(c) causing a coacervate of the hydrophilic polymers to separate from the sol and to deposit around the particles of primary emulsion at a temperature above the gel point of the gelable polymer; and

(d) hardening the coacervate deposit so formed by lowering the temperature below the gel point of the gelable wall-forming polymer.

9. The process of claim 8 wherein the coacervate is formed by introducing the primary emulsion and the aqueous sol of the hydrophilic polymer into an aqueous solution of a coacervating agent.

10. The process 'for coating particles of an aqueous liquid-in-oil emulsion by coacervation which comprises: (1) forming a primary aqueous liquid-in-oil emulsion containing in the oil phase a material selected from the group consisting of non-ionic surface active agents, waxes, solid fats and sterols, and (2) mixing together the said primary emulsion, an aqueous sol of a gelable hydrophilic colloid, and the coacervating agent, at a temperature above the gel point of the said colloid, to produce a secondary emulsion in which the intact emulsion particles are coated by the rapidly-formed coacervate.

11. The process for coating particles of an aqueous liquid-in-oil emulsion by coacervation which comprises: (1) forming a primary aqueous liquid-in-oil emulsion containing in the oil phase a material selected from the group consisting of non-ionic surface active agents, waxes, solid fats and sterols, and containing in the aqueous liquid phase a water-thickening agent substantially insoluble in the oil phase and capable of increasing the viscosity of the aqueous phase, (2) mixing together the said primary emulsion, an aqueous sol of a gelable hydrophilic colloid, a water-thickening agent as above described, and a coacervating agent, at a temperature above the gel point of the said colloid, to produce a secondary emulsion in which the intact emulsion particles are coated by the rapidly-formed coacervate, (3) cooling the coacervate-coated particles to the gel point of the said colloid, (4) separating the cooled coacervate-coated particles, and (5) drying the separated coacervate coated particles to obtain a product having an essentially dry surface.

12. The process for coating particles of an aqueous liquid-in-oil emulsion by coacervation which comprises: (1) forming an aqueous liquid-in-oil emulsion containing. hydrogenated castor oil in the oil phase and methyl cellulose in the aqueous liquid phase, (2) mixing together the said primary emulsion, methyl cellulose, gelatin and sodium sulfate, at a temperature above about 50 C., to produce a secondary emulsion in which the intact primary emulsion particles are coated by the rapidly-formed coacervate, (3) cooling the coacervate-coated particles to about 5 C., (4) separating the cooled coacervate-coated particles, and (5) drying the separated coacervate-coated particles to obtain a product having an essentially dry surface.

13. An aqueous liquid-in-oil emulsion enclosed in a coacervate coating, the said coacervate containing a single gelable hydrophilic colloid.

14. An aqueous liquid-in-oil emulsion enclosed in an essentially dry coacervate coating, the oil phase of the said emulsion containing a material selected from the group consisting of non-ionic surface active agents, waxes, solid fats and sterols, the said coacervate containing a single gelable hydrophilic colloid.

15. An aqueous liquid-in-oil emulsion enclosed in an essentially dry gelating coacervate coating, the oil phase of the said emulsion containing a material selected from the group consisting of non-ionic surface active agents, waxes, solid fats and sterols, the aqueous liquid phase of the said emulsion containing a water-thickening agent.

16. An aqueous liquid-in-oil emulsion enclosed in an essentially dry gelatin coacervate coating, the oil phase of the said emulsion containing hydrogenated castor oil and the liquid phase of the said emulsion containing methyl cellulose.

17. The process for coating particles of an aqueous liquid-in-oil emulsion by coacervation which comprises: (1) forming a primary aqueous liquid-in-oil emulsion containing in the oil phase a material selected from the group consisting of non-ionic surface active agents, waxes, solid fats and sterols, and (2) mixing together the said primary emulsion, an aqueous sol of at least two hydrophilic colloids, at least one of which is gelable and at least one of which is isoelectric, at a temperature above the gel point of the said gelable colloid, to produce a secondary emulsion( and (3) causing a coacervate to deposit about the particles of the sa d S condary emulsion.

18. The process for coating particles of an aqueous liquid-in-oil emulsion by coacervation which comprises: (1) forming a primary aqueous liquid-in-oil emulsion containing in the oil phase a material selected from the group consisting of non-ionic surface active agents, waxes, solid fats and sterols, and containing in the aqueous liquid phase a water-thickening agent substantially insoluble in the oil phase and capable of increasing the viscosity of the aqueous phase, (2) mixing together the said primary emulsion, an aqueous sol of at least two hydrophilic colloids, at least one of Which is gelable and at least one of which is isoelectric, at a temperature above the gel point of the said gelable colloid, to produce a secondary emulsion, (3) causing a coacervate to deposit about the particles of the said secondary emulsion, (4) cooling the coacervate-coated particles to the gel point of the said gelable colloid, (5) separating the cooled coacervate-coated particles, and (6) drying the separated coacervated-coated particles to obtain a product having an essentially dry surface.

19. The process for coating particles of an aqueous liquid-in-oil emulsion by coacervation which comprises: (1) forming an aqueous liquid-in-oil emulsion containing hydrogenated castor oil in the oil phase and methyl cellulose in the aqueous liquid phase, (2) mixing together the said primary emulsion, gelatin and acacia, at a temperature above about C., (3) diluting the said secondary emulsion with water to cause a coacervate to deposit about the particles of the said second emulsion, (4) cooling the coacervate-coated particles to about 5 C., (5) separating the cooled coacervate-coated particles, and (6) drying the separated coacervate-coated particles to obtain a product having an essentially dry surface.

20. An aqueous liquid-in-oil emulsion enclosed in a coactervate coating, the said coacervate containing at least two hydrophilic colloids, at least one of which is gelable and at least one which is isoelectric.

21. An aqueous liquid-in-oil emulsion enclosed in an essentially dry coacervate coating, the oil phase of the said emulsion containing a material selected from the group consisting of non-ionic surface active agents, waxes, solid fats and sterols, the said coacervate containing at least two hydrophilic colloids, at least one of which is gelable and at least one of which is isoelectric.

22. An aqueous liquid-in-oil emulsion enclosed in an essentially dry coacervate coating, the oil phase of the said emulsion containing a material selected from the group consisting of non-ionic surface active agents, waxes, solid fats and sterols, the aqueous liquid phase of the said emulsion containing a water-thickening agent, the said coacervate coating containing at least two hydrophilic colloids, at least one of which is gelable and at least one of which is isoelectric.

23. An aqueous liquid-in-oil emulsion enclosed in an essentially dry gelatin and acacia coacervate coating, the oil phase of the said emulsion containing hydrogenated castor oil and the liquid phase of the said emulsion containing methyl cellulose.

24 The process for coating particles of a hydrophilic liquid-in-oil emulsion by coacervation which comprises: (1) forming a primary hydrophilic liquid-in-oil emulsion containing an anti-inversion agent in the oil phase, and (2) forming a secondary emulsion comprising the said pri mary emulsion, an aqueous dispersion of a linear macromolecular synthetic polymer, and a material selected from the group consisting of aqueous solutions of ionizable salts and water-soluble liquids in which the said polymer is less soluble than in water, whereupon a coacervate forms about the particles of the said secondary emulsion.

25. The process for coating particles of a hydrophilic liquid-in-oil emulsion by coacervation which comprises: (1) forming a primary hydrophilic liquid-in-oil emulsion containing an anti-inversion agent in the oil phase and a thickening agent in the hydrophilic liquid phase, and (2) forming a secondary emulsion comprising the said primary emulsion, an aqueous dispersion of a linear macromolecular synthetic polymer, and a material selected from the group consisting of aqueous solutions of ionizable salts and water-soluble liquids in which the said polymer is less soluble than in water, whereupon a coacervate forms about the particles of the said secondary emulsion.

26. The process for coating particles of an aqueous liquid-in-oil emulsion by coacervation which comprises: (1) forming a primary aqueous liquid-in-oil emulsion containing an anti-inversion agent in the oil phase and a thickening agent in the aqueous phase, (2) forming a secondary emulsion comprising the said primary emulsion, an aqueous dispersion of a linear macromolecular synthetic polymer, and a material selected from the group consisting of aqueous solutions of ionizable salts and water-soluble liquids in which the said polymer is less soluble than in water, whereupon a coacervate forms about the particles of the said secondary emulsion, (3) lowering the pH of the resulting mixture to less than about 2, and (4) drying the coacervate to obtain a product having an essentially dry surface.

27. The process for coating particles of an aqueous liquid-in-oil emulsion by coacervation which comprises: (1) forming a primary aqueous liquid-in-oil emulsion containing hydrogenated castor oil in the oil phase and methyl cellulose in the aqueous phase, (2) forming a secondary emulsion comprising the said primary emulsion, an aqueous dispersion of styrene maleic acid copolymer, and sodium sulfate, at a temperature of about 80 C., whereupon a coacervate forms about the particles of the said secondary emulsion, (3) lowering the pH of the resulting mixture to less than about 2 to harden the coacervate, (4) washing the thus-hardened coacervate, and (5) drying the coacervate to obtain a product having an essentially dry surface.

29. A hydrophilic liquid-in-oil emulsion substantially enclosed in a coacervate coating, the oil phase of the said emulsion containing an anti-inversion agent, the hydrophilic liquid phase containing a thickening agent, and the said coacervate containing a linear macromolecular synthetic polymer.

30. An aqueous liquid-in-oil emulsion substantially enclosed in a coacervate coating, the oil phase of the said emulsion containing an anti-inversion agent, the aqueous phase of the said emulsion containing a thickening agent, and the said coacervate containing a linear macromolecular synthetic polymer.

31. An aqueous liquid-in-oil emulsion substantially enclosed in a coacervate coating, the oil phase of the said emulsion containing hydrogenated castor oil, the aqueous phase of the said emulsion containing methyl cellulose, and the said coacervate containing styrene maleic acid copolymer.

32. The process for coating particles of a hydrophilic liquid-in-oil emulsion by coacervation which comprises: (1) forming a primary hydrophilic liquid-in-oil emulsion containing an anti-inversion agent in the oil phase, (2) forming a secondary emulsion comprising the said primary emulsion and an aqueous dispersion of at least one hydrophilic colloid and at least one linear macromolecular synthetic polymer, and (3) causing a coacervate to deposit about particles of the said secondary emulsion.

33. The process for coating particles of a hydrophilic liquid-in-oil emulsion by coacervation which comprises: 1) forming a primary hydrophilic liquid-in-oil emulson containing an anti-inversion agent in the oil phase and a thickening agent in the hydrophilic liquid phase (2) forming a secondary emulsion comprising the said primary emulsion and an aqueous dispersion of at least one hydrophilic colloid and at least one linear macromolecular synthetic polymer, and (3) adjusting the pH to cause a coacervate to deposit about the particles of the said secondary emulsion.

34. The process for coating particles of a hydrophilic liquid-in-oil emulsion by coacervation which comprises: (1) forming a primary hydrophilic liquid-in-oil emulsion containing an anti-inversion agent in the oil phase and a thickening agent in the hydrophilic liquid phase, (2) forming a secondary emulsion comprising the said primary emulsion and an aqueous dispersion of at least one gelable hydrophilic colloid and at least one linear macromolecular synthetic polymer, at a temperature above the gel point of the said gelable colloid, (3) adjusting the pH to cause a coacervate to deposit about the particles of the said secondary emulsion, (4) cooling the said coacervate at least to the gel point of the said gelable colloid, (5) separating the cooled coacervate, and (6) drying the separated coacervate to obtain a product having an essentially dry surface.

35. The process for coating particles of an aqueous liquid-in-oil emulsion by coacervation which comprises: forming an aqueous liquid-in-oil emulsion containing hydrogenated castor oil in the oil phase and methyl cellulose in the aqueous phase, (2) forming a secondary emulsion comprising the said primary emulsion, gelatin and styrene maleic acid copolymer, at a temperature above about C., (3) adjusting the pH to cause a coacervate to deposit about the particles of the said secondary emulsion, (4) cooling the said coacervate to about 5 (3., (5) separating the cooled coacervate, and (6) drying the separated c0- acervate to obtain a product having an essentially dry surface.

36. A hydrophilic liquid-in-oil emulsion substantially enclosed in a complex coacervate coating, at least one component of which is a hydrophilic colloid and at least one component of which is a linear macromolecular synthetic polymer.

37. A hydrophilic liquid-in-oil emulsion substantially enclosed in a complex coacervate coating, at least one component of which is a gelable hydrophilic colloid and at least one component of which is a linear macromolecular synthetic polymer, the oil phase of the enclosed emulsion containing an anti-inversion agent and the hydrophilic liquid phase containing a thickening agent.

38. An aqueous liquid-inoil emulsion substantially enclosed in a complex coacervate coating, the coacervating components of the said coating being gelatin and styrene maleic acid copolymer, the oil phase of the encapsulated emulsion containing hydrogenatd castor oil and the aqueous phase containing methyl cellulose.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 13 line 47 after "hydrolysis" insert can be partial or complete and involves a conversion Column 14 line 71, "corbitan" should read sorbitan Signed and sealed this 4th day of May 1971 WILLIAM E. Commissioner of Paten SCHUYLER,